Charge-coupled devices (CCDs) and complementary metal-oxide-semiconductor (CMOS) devices are commonly used as image sensors in digital imaging devices such as digital cameras. A CCD or CMOS image sensor typically includes a matrix of pixels, where each pixel includes a photodiode formed by a doped region of semiconductor in a semiconductor substrate, and a gate electrode. The photodiode collects the charge produced by the incident light around the biased gate electrode. A mechanical or electronic shutter function is used to start and stop charge accumulation in the pixels. Voltage or current values representing the accumulated charges are then shifted off the pixel array, amplified and processed to produce data representing an image.
An important factor in the design of an image sensors requiring precise global shuttering for time of flight sensors or high speed cameras requires precisely-matched signal propagation delay. Signal propagation delays that are too long or that are unequal through the sensor can adversely affect performance of the sensor. Another important factor is low resistivity contact between the electronic gating signal and the gated. A CCD or CMOS image sensor is typically made of multiple layers, including one or more semiconductor layers, one or more insulation layers and one or more conductive layers. Poor electrical contact between certain layers can cause poor performance of the device.